The present invention generally relates to an electrochemical cell and, more particularly, relates to a high rate capable electrochemical cell having an increased anode-to-cathode interface surface area.
Electrochemical cells are commonly employed to supply voltage for electrically operated devices, and particularly for portable electrically operated devices. Currently, the popular alkaline cells of the generally cylindrical type are commercially available in industry standard sizes including D-, C-, AA-, AAA-, and AAAA-size cells, as well as other sizes and configurations. Electrochemical cells, such as the aforementioned type, commonly provide a predetermined open circuit voltage supply.
Conventional cylindrical alkaline cells generally have a cylindrical-shaped steel can provided with a positive cover at one end and a negative cover at the opposite end. The cylindrical cell has a positive electrode, commonly referred to as the cathode, which is often formed of a mixture of manganese dioxide, graphite, potassium hydroxide solution, deionized water, and a TEFLON.RTM. solution formed about the interior side surface of the cylindrical steel can. A cup-shaped separator is generally centrally disposed in an inner cylindrical volume of the can about the interior surface of the cathode. A negative electrode, commonly referred to as the anode, is typically formed of zinc powder, a gelling agent, and other additives, and is disposed within the separator. An electrolyte solution is also disposed in the can. One example of a conventional cylindrical cell is disclosed in U.S. Pat. No. 5,501,924, which is hereby incorporated by reference.
Conventional cells of the aforementioned cylindrical type commonly have a single anode and a single cathode contained within the steel can, with the separator interfaced between the two electrodes. With the bobbin type cell construction, the cathode is disposed adjacent the inner wall of the steel can, while the anode is disposed within a cylindrical volume centrally formed in the cathode. Accordingly, the separator has an anode-to-cathode interface surface area generally defined by the shape and size of the anode and the cathode. With the conventional bobbin type cell, the anode-to-cathode interface surface area is approximately equal to the surface defining the periphery of the cylindrical anode.
Another cell construction, commonly referred to as the jelly-roll cell construction, employs a sheet of anode and a sheet of cathode tightly wound together with a separator interdisposed between the two electrode sheets. While conventional jelly-roll wound cells offer high rate capability with a large anode-to-cathode interface area, such cells have inherent limitations. For instance, the process of forming jelly-roll cells is time consuming and relatively expensive. Further, the jelly-roll separator consumes a relatively large amount of available volume, thereby compromising the volume that remains for active cell materials.
A primary goal in designing alkaline cells is to increase the service performance which is the length of time for the cell to discharge under a given load to a specific voltage at which the cell is no longer useful for its intended purpose. Commercially available alkaline cells have an external size that is defined by industry standards, thereby limiting the ability to increase the amount of active materials that can be utilized. Conventional approaches for improving high rate performance have focused on increasing the efficiency of the internal cell materials. The need for high rate capable cells is becoming even more important with the increasing demand from consumers using high tech, high drain electronics devices. To meet this demand, the need to find ways to increase high rate service performance remains a primary goal of the cell designers.